Hundreds of men — all black and many of them poor — signed up. Some of the men thought they were being treated for rheumatism or bad stomachs. They were promised free meals, free physicals and free burial insurance.

What the signs never told them was they would become part of the “Tuskegee Study of Untreated Syphilis in the Negro Male,” a secret experiment conducted by the U.S. Public Health Service to study the progression of the deadly venereal disease — without treatment.

On Tuesday, the Tuskegee History Center will mark the 20th anniversary of its founding and President Bill Clinton’s apology to the survivors of the experiment with a day-long program devoted to the fallout of the study. It destroyed the trust many African Americans held for medical institutions — a legacy that persists today.

“These anniversaries offer a unique opportunity for us to remind America and the world of the medical injustice that occurred here in Macon County,” said Fred Gray, the civil rights attorney who brought a class-action lawsuit on behalf of unwitting study participants. “We have to continue to tell their story so that such injustices never happen again.”

Herman Shaw, one of the last survivors of the Tuskegee study, raises his arms with praise as President Bill Clinton apologizes for the infamous experiment. (Susan Biddle/Washington Post)

The study recruited 600 black men, of which 399 were diagnosed with syphilis and 201 were a control group without the disease. The researchers never obtained informed consent from the men and never told the men with syphilis that they were not being treated but were simply being watched until they died and their bodies examined for ravages of the disease.

“So I went over, and they told me I had bad blood,” Pollard remembered. “And that’s what they’ve been telling me ever since. They come around from time to time and check me over and they say, ‘Charlie, you’ve got bad blood.’ ”

In the book, Herman Shaw, a farmer, recounted hearing about the study as a kind of health care program. “People said you could get free medicine for yourself and things of that kind, and they would have a meeting at Salmon Chapel at a certain date.” So he went.

Initially, when the study began, treatment for syphilis was not effective, often dangerous and fatal. But even after penicillin was discovered and used as a treatment for the disease, the men in the Tuskegee study were not offered the antibiotic.

“All I knew was that they just kept saying I had the bad blood — they never mentioned syphilis to me. Not even once,” said Pollard, who added: “They been doctoring me off and on ever since then. And they gave me a blood tonic.”

Shaw explained: “We got three different types of medicine. A little round pill — sometime a capsule — sometime a little vial of medicine — everybody got the same thing.”

Although originally projected to last six months, the study extended for 40 years. “Local physicians asked to assist with study and not to treat men,” the Centers for Disease Control reported in a timeline of the experiment. “Decision was made to follow the men until death.”

Eunice Rivers, a local nurse, was recruited by doctors to serve as a recruiter and conduit between researchers and the men. Nurse Rivers, as she became known, kept records of the men and drove them to government doctors when they visited the community. She took them to doctors’ appointments in “a shiny station wagon with the government emblem on the front door, according to “Bad Blood.” On one occasion, she followed a man to a private doctor to make sure he did not receive treatment.

In 1945, according to the CDC timeline, penicillin was “accepted as treatment of choice for syphilis.” The U.S. Public Health Services created what they called “rapid treatment centers” to help men afflicted with syphilis — except the men in the Tuskegee study.

In 1966, a public health service investigator raised concerns about the study. Peter Buxtun wrote to the director of the U.S. division of venereal diseases about the ethics of the experiment. But the agency ignored Buxtun’s concerns.

Buxtun eventually leaked information about the study to an Associated Press reporter named Jean Heller, who years later called it “one of the grossest violations of human rights I can imagine.” On July 26, 1972, Heller’s story appeared on the front page of the New York Times, revealing that the men had deliberately been left untreated for 40 years.

On May 16, 1997, President Bill Clinton issued an apology to the eight remaining survivors of the experiment:

“The United States government did something that was wrong — deeply, profoundly, morally wrong,” Clinton said. “It was an outrage to our commitment to integrity and equality for all our citizens. To the survivors, to the wives and family members, the children and the grandchildren, I say what you know: No power on Earth can give you back the lives lost, the pain suffered, the years of internal torment and anguish. What was done cannot be undone. But we can end the silence. We can stop turning our heads away. We can look at you in the eye and finally say on behalf of the American people, what the United States government did was shameful, and I am sorry.”